The present invention is generally directed to an information retrieval system of the type which automatically retrieves selected information bearing elements for inspection. The present invention is more particularly directed to an improved scanning means with ramp speed control for an automatic film searching and retrieval system for use with film having a plurality of consecutively numbered frames, and wherein each frame includes an information image and an adjacent frame marker.
Information retrieval systems are well known. One efficient type of retrieval system that has found widespread acceptance is often referred to as a microfilm retrieval system. In such systems, copies of documents and/or data are recorded on film such as 16 mm film wherein each film frame comprises an information bearing element. With the size of the film frame being on the order of 1 mm per document inch, such size reduction affords a substantial reduction in information storage volume and greatly simplifies handling of the information. Such a reduction in size necessarily precludes direct reading of the information bearing elements or film frames and the usual procedure for reading them is to project the film frame images onto a screen and to magnify them to a size corresponding approximately to the original size of the information document that is recorded.
Because literally thousands of information bearing elements or film frames comprise a roll of microfilm, searching for a particular image film frame can be time consuming. As an example, microfilm reels are known to include information bearing elements or frames on the order of 40,000 frames per reel. To provide ready access to a preselected information bearing element or film frame, automatic search techniques have been developed in the form of automatic retrieval systems.
In such systems, the film frames of the microfilm reels are numbered consecutively for identification and each film frame has an adjacent marker which may be sensed so that as the film frames are scanned they may be counted and the identification numbers displayed. Hence, during the scan cycle, the counter provides the current number of the film frame currently being sensed and at the end of a scan cycle, provides the current number of the film frame being inspected.
Retrieval systems also include a means for entering a target number which identifies the film frame to be inspected. Suitable logic control within the retrieval systems determines from the current number and the target number whether the film is to be driven in an up direction or a down direction to arrive at the preselected film frame to be inspected.
Scanning systems of the prior art have utilized various techniques for stopping the film when the preselected film frame has been located. Such techniques have included film handling apparatus which move the film at a relatively low rate of speed when searching for a preselected film frame to avoid breakage of the film when it is stopped. Other systems have utilized high speed motors for driving the film at high speed and means for detecting when the preselected image frame is a given number of frames away from the currently sensed frame to switch over to a low speed motor for driving the film at low speed for a predetermined number of frames until the selected film frame is located.
Unfortunately, such prior systems have not been totally reliable. Such systems are either slow, or are subject to overshoot, and should overshoot occur, they generally do not include means for compensating for overshoot to reverse direction and arrive at the selected film frame. When such overshoot protection is afforded, such overshoot protection is provided by complex circuitry which is generally expensive compared to the limited use of such protective circuitry.
Lastly, prior systems of the type referred to above, do not afford accurate control for the stopping of the film in relation to the adjacent film marker and the frame marker sensors. As a result, inaccurate counting of the film frames during subsequent searches may occur with consequent searching error.
It is, therefore, an object of the present invention to provide a new and improved scanning means for an information retrieval system which provides the automatic locating of a preselected information bearing element which is capable of driving the information bearing elements at a high rate of speed but yet affording accurate stopping of the information bearing element scan upon the location of the preselected information bearing element.
It is a more particular object of the present invention to provide a scanning means for information retrieval systems which is capable of efficiently locating a preselected information bearing element regardless of the spacing between information bearing elements.
It is a still further object of the present invention to provide a new and improved scanning means for an information retrieval system wherein the system is relatively uncomplicated and yet is capable of utilizing overshoot to its advantage during the search cycle.